Applicant's U.S. Pat. No. 4,060,869 (the '869 patent) discloses a hydraulically operated apparatus for permanently enlarging selected sections of footgear so as to accommodate the individual characteristics of the user's foot. The device comprises a generally cylindrical member having a bore which supports diametrically opposed domed members in a piston/cylinder relationship. Hydraulic pressure is supplied to the chamber intermediate the inner ends of the two pistons, so that the domed members are forced outwardly against selected portions of the interior of the article of footwear, deforming this so that it will better accommodate the user's foot. The end surfaces of the domed members are configured to bear directly against the interior surface of the shoe/boot, and the hydraulic pressure is supplied from a bench-operated reciprocating hydraulic pump (resembling a bottle jack), a compressed air cylinder, or a similar remote source.
The apparatus which is disclosed in the '869 patent has proven to be extremely effective and highly popular, especially for form-fitting ski boots. The device has been found particularly suitable for this type of service, in that, owing to the high pressures which can be generated by the hydraulic pump, compressed air cylinder or other remote source, it is capable of exerting the relatively high contact pressures which are required to stretch the comparatively rigid materials of which ski boots are constructed and also due to the fact that most such work is conducted in a workshop environment (i.e., in a ski shop) which ordinarily includes a workbench on which the hydraulic pump can be operated, and/or space in which a compressed air cylinder can be accommodated, and in which the slight leakages of conventional hydraulic fluid which occasionally accompany operation of the device do not present an unacceptable problem.
In other environments and applications, however, the device which is disclosed in the '869 patent has been found to have its limitations. For example, in a typical retail environment where men's/ladies' street shoes are sold, the presence/operation of a compressed gas cylinder or manually-reciprocated hydraulic pump is ordinarily inappropriate, and furthermore there is typically insufficient space in which to locate such pressure sources. Moreover, the leakage of oily hydraulic fluid, while perhaps acceptable in a shop environment, and to which synthetic ski boot materials are relative impervious, is highly objectionable in a retail setting. In short, the apparatus which is disclosed in the '869 patent is inappropriate or at least inconvenient for use on the sales floor of a typical shoe store.
Furthermore, the street shoes which are usually sold in such environments do not require the same level of stretching pressure as do ski boots. For example, the relatively thin leather of a lady's high-heeled shoe can be permanently deformed by the application of contact pressures which are far lower than those which are required to stretch an ordinary ski boot. Moreover, the permanent deformation of relatively lightweight leathers usually does not require the same application of heat as is needed for the relatively stiff materials of which ski boots and other relatively heavyweight footwear are constructed (e.g., see FIG. 3 of the '869 patent).
Another limitation of the device which is disclosed in the '869 patent is that it exerts pressure only over a relatively limited, generally oval area which is defined by the contact surface of the domed piston member. This suffices in many cases where comparatively high contact pressures need to be concentrated at a particular point on the user's foot (at the location of an ankle bone, for example), such as are commonly encountered with ski boots. By contrast, a more widely distributed pressure is typically needed when working with street or dress shoes, where a more generalized area of the shoe usually needs to be enlarged, such as across the toe box or arch, or heel areas (the first being the more common situation).
Another relevant factor is that the widths of the shoes which are on sale in a typical retail environment usually vary over a relatively large range, whereas the maximum variation in the width between the domed members of the device which is disclosed in the '869 patent is limited to the combined travel of the piston members; this makes it difficult or impossible for the device to accommodate the full range of shoe size which are commonly on hand, particularly since the angle at which the axes of the domed pistons intercept the interior walls of the shoes tends to vary greatly with the width, especially (for example) in the tapering toe box area. A related deficiency of the prior device is that any pivoting movement of the knurled surface of the domed members which occurs as the pistons extend tends to cause significant abrasion or damage to the interior of the shoe, particularly if this is formed of a soft liner leather of the type which are commonly used in dress shoes.
Accordingly, there exists a need for a compact stretching tool which can be used in a retail or similar environment, to enlarge predetermined areas of shoes and other footwear so as to accommodate the requirements of the individual user's feet. Moreover, there is a need for such an apparatus which can be conveniently adapted to work with shoes having a wide range of sizes and widths, and which can distribute the stretching force over a relatively large internal area of the shoe. Still further, there is a need for such a tool which can function without the possibility of leaking hydraulic fluid or other material which would be objectionable in a retail environment.